Liquid crystal display device with negative retardation of retardation plates being approximately zero.

ABSTRACT

A liquid crystal display device includes a liquid crystal cell, polarizers, a first retardation plate arranged between the liquid crystal cell and the first polarizer, and a second retardation plate arranged between the liquid crystal cell and the second polarizer. Each retardation plate has an optical axis in a plane parallel to the substrate surface and a retardation of substantially λ/4. The optical axis of one retardation plate is perpendicular to the optical axis of the other. The polarizing axes of the polarizers are arranged at an angle of 45° with respect to the optical axes of the retardation plates. The liquid crystal cell is arranged such that a state of alignment of liquid crystal molecules changes, accompanying a change in a polar angle and/or change in an azimuth, upon application of a voltage.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display device havingan improved viewing angle characteristic.

2. Description of the Related Art

In a liquid crystal display device, it is well known that the contrastof the display in the case of taking an oblique view of the image areais different from the contrast of the display in the case of taking afront view of the image area (the viewing angle characteristic).Therefore, there is a demand for a liquid crystal display device havingan improved viewing angle characteristic.

Japanese Unexamined Patent Publications No. 1-270024 and No. 2000-29010disclose a liquid crystal display device including a vertical alignmenttype liquid crystal cell, first and second polarizers arranged on eitherside of the liquid crystal cell, a first λ/4 plate arranged between theliquid crystal cell and the first polarizer, and a second λ/4 platearranged between the liquid crystal cell and the second polarizer. Whenthe polarizers and the λ/4 plates are arranged as described above, it ispossible to improve the viewing angle characteristic in the case oftaking an oblique viewing of the image area.

However, although the viewing angle characteristic of the liquid crystaldisplay device having the polarizers and λ/4 plates can be improved, therange of the viewing angle, in which a viewer can see the display withhigh contrast, is relatively small.

Also, as a technique for improving the viewing angle characteristic ofthe liquid crystal display device, there is provided a technique ofalignment division. In the technique of alignment division, one pixel isdivided into a plurality of regions or domains, the states of alignmentof which are different from each other, so that a viewer can see adisplay with high contrast even when the viewer takes an oblique view ofthe image area in the same manner as that when the viewer takes a frontview of the image area. Especially, the assignee of the presentapplication proposes a vertical alignment type liquid crystal displaydevice having structures or slits which linearly extend on or inelectrodes on the substrates between which the liquid crystal layer isinterposed.

In this liquid crystal display device, most of the liquid crystalmolecules are aligned substantially perpendicularly to the substratesurfaces when a voltage is not applied. However, liquid crystalmolecules located close to the structure or slit tend to be alignedperpendicular to the wall surface of the structure or slit andpre-tilted with respect to the substrate surface. When voltage isapplied, liquid crystal molecules located close to the structure or slitare inclined according to the pre-tilt so that they are inclined to apredetermined direction. Therefore, most of the liquid crystal moleculesare inclined according to the liquid crystal molecules located close tothe structure or slit.

The direction of alignment of liquid crystal molecules located on oneside of the structure or slit is opposite to the direction of alignmentof liquid crystal molecules located on the other side of the structureor slit. Therefore, two regions, the directions of alignment of whichare different from each other, are formed on either side of thestructure or slit. Therefore, even if rubbing is not conducted on theliquid crystal display device, it is possible to realize the alignmentdivision similar to that of the liquid crystal display device in whichpre-tilt is provided by rubbing. Therefore, when alignment division isconducted as described above, it is possible to obtain a viewing anglecharacteristic in which the viewing angle range is wide and the contrastis high. The liquid crystal display device having alignment division isdisclosed, for example, in Japanese Unexamined Patent Publication No.11-352489.

Japanese Patent No. 2945143 discloses a liquid crystal display device inwhich a polymer dispersed type liquid crystal display device isinterposed between polarizers in a Cross Nicol arrangement. JapaneseUnexamined Patent Publication No. 2000-347174 discloses a network-likepolymer dispersed type liquid crystal display device.

In the above described liquid crystal display device having alignmentdivision, the state of alignment of most liquid crystal molecules in onepixel is approximately controlled according to the predeterminedstructures or slits when voltage is applied. However, sometimes, thestate of alignment of a portion of the liquid crystal molecules in onepixel cannot be controlled according to the predetermined structures orslits. For example, liquid crystal molecules located close to the buslines located in the periphery of the pixel tend to be alignedperpendicularly to the wall surface of the bus lines. Therefore, thestate of alignment of the liquid crystal molecules is different from thestate of alignment of the liquid crystal molecules controlled accordingto the predetermined structures or slits, which could be a cause ofdeterioration of brightness. Liquid crystal molecules on thepredetermined structures or slits are aligned in parallel to thepredetermined structures or slits. The polarizers are arranged so thatthe axes of polarization can form an angle of 45° with respect to thedirector of the liquid crystal molecules when voltage is applied.However, a portion of the liquid crystal molecules become parallel tothe axis of polarization, which could be a cause of deterioration ofbrightness.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a liquid crystaldisplay device by which a viewer can see an excellent image area over awide viewing angle and which provides for high brightness.

According to the first aspect of the present invention, there isprovided a liquid crystal display device comprising a liquid crystalcell comprising a pair of substrates and a liquid crystal layer arrangedbetween the pair of substrates, first and second polarizers arranged oneither side of the liquid crystal cell, a first retardation platearranged between the liquid crystal cell and the first polarizer, and asecond retardation plate arranged between the liquid crystal cell andthe second polarizer. Each of the first and second retardation plateshas an optical axis in a plane parallel to the surfaces of thesubstrates, and a retardation of substantially λ/4. The optical axis ofthe first retardation plate is perpendicular to the optical axis of thesecond retardation plate, and the first and second polarizers havepolarizing axes arranged at an angle of 45° with respect to the opticalaxes of the first and second retardation plates. The liquid crystal cellis arranged such that a state of alignment of the liquid crystalmolecules changes, accompanying change in a polar angle and/or change inan azimuth upon application of voltage.

According to the above arrangement, it is possible to provide a liquidcrystal display device by which a viewer can see an excellent image areaover a wide viewing angle and which provides for high brightness.

Also, if an azimuth angle distribution is provided in the state ofalignment of liquid crystal molecules when the liquid crystal moleculesare arranged horizontally or obliquely with respect to the substratesurfaces, the transmittance can be improved.

According to the second aspect of the present invention, there isprovided a liquid crystal display device comprising a liquid crystalcell comprising a pair of substrates and a liquid crystal layer arrangedbetween the pair of substrates, first and second polarizers arranged oneither side of the liquid crystal cell, a first retardation platearranged between the liquid crystal cell and the first polarizer, and asecond retardation plate arranged between the liquid crystal cell andthe second polarizer. Each of the first and second retardation plateshas an optical axis in a plane parallel to the surfaces of thesubstrates, and a retardation of substantially λ/4. The optical axis ofthe first retardation plate is perpendicular to the optical axis of thesecond retardation plate. The first and second polarizers havepolarizing axes arranged at an angle of 45° with respect to the opticalaxes of the first and second retardation plates. The liquid crystal ofthe liquid crystal cell is of a vertical alignment type, the liquidcrystal cell includes structures or slits arranged on or in an electrodeof at least one of the substrates, and a state of alignment of theliquid crystal molecules located on one side of the structure or slit isdifferent from a state of alignment of the liquid crystal moleculeslocated on the other side of the structure or slit. At least one of thepair of substrates has electrically conductive linear structures.

According to the above arrangement, it is possible to provide a liquidcrystal display device by which a viewer can see an excellent image areahaving a wide viewing angle and which provides for a high brightness.

According to the third aspect of the present invention, there isprovided a liquid crystal display device comprising a liquid crystalcell comprising a pair of substrates and a liquid crystal layer arrangedbetween the pair of substrates, first and second polarizers arranged oneither side of the liquid crystal cell, a first retardation platearranged between the liquid crystal cell and the first polarizer, and asecond retardation plate arranged between the liquid crystal cell andthe second polarizer. Each of the first and second retardation plateshas an optical axis in a plane parallel to the surfaces of thesubstrates, and a retardation of substantially λ/4. The optical axis ofthe first retardation plate is perpendicular to the optical axis of thesecond retardation plate. The first and second polarizers havepolarizing axes arranged at an angle of 45° with respect to the opticalaxes of the first and second retardation plates. The liquid crystal ofthe liquid crystal cell is of a vertical alignment type, the liquidcrystal cell includes structures or slits arranged on or in an electrodeof at least one of the substrates, and a state of alignment of theliquid crystal molecules located on one side of the structure or slit isdifferent from a state of alignment of the liquid crystal moleculeslocated on the other side of the structure or slit. A retardation in theplane of the retardation plate is not less than 120 μm and not more than160 μm.

According to the above arrangement, it is possible to provide a liquidcrystal display device by which a viewer can see an excellent image areaover a wide viewing angle and which provides for a high contrast.

According to the fourth aspect of the present invention, there isprovided a liquid crystal display device comprising a liquid crystalcell comprising a pair of substrates and a liquid crystal layer arrangedbetween the pair of substrates and a film causing light to scatter in aspecific direction. Liquid crystal of the liquid crystal cell is of avertical alignment type, the liquid crystal cell includes structures orslits arranged on or in an electrode of at least one of the substrates,and a state of alignment of the liquid crystal molecules located on oneside of the structure or slit is different from a state of alignment ofthe liquid crystal molecules located on the other side of the structureor slit.

According to the above arrangement, it is possible to provide a liquidcrystal display device by which a viewer can see an excellent image areaover a wide viewing angle and which provides for a high brightness.

According to the fifth aspect of the present invention, there isprovided a liquid crystal display device comprising a liquid crystalcell comprising a pair of substrates and a liquid crystal layer arrangedbetween the pair of substrates, first and second polarizers arranged oneither side of the liquid crystal cell, a first retardation platearranged between the liquid crystal cell and the first polarizer, and asecond retardation plate arranged between the liquid crystal cell andthe second polarizer. Each of the first and second retardation plateshas an optical axis in a plane parallel to the surfaces of thesubstrates and a retardation of substantially λ/4. The optical axis ofthe first retardation plate is perpendicular to the optical axis of thesecond retardation plate. The first and second polarizers havepolarizing axes arranged at an angle of 45° with respect to the opticalaxes of the first and second retardation plates. The liquid crystallayer of the liquid crystal cell contains liquid crystal and resincoexisting with the liquid crystal.

According to the above arrangement, it is possible to provide a liquidcrystal display device by which a viewer can see an excellent image areaover a wide viewing angle and which provides for a high brightness.

According to the sixth aspect of the present invention, there isprovided a liquid crystal display device comprising a liquid crystalcell comprising a pair of substrates and a liquid crystal layer arrangedbetween the pair of substrates, first and second polarizers arranged oneither side of the liquid crystal cell, a first retardation platearranged between the liquid crystal cell and the first polarizer, and asecond retardation plate arranged between the liquid crystal cell andthe second polarizer. Each of the first and second retardation plateshas an optical axis in a plane parallel to the surfaces of thesubstrates and a retardation of substantially λ/4. The optical axis ofthe first retardation plate is perpendicular to the optical axis of thesecond retardation plate. The first and second polarizers havepolarizing axes arranged at an angle of 45° with respect to the opticalaxes of the first and second retardation plates. The liquid crystal ofthe liquid crystal cell is of a vertical alignment type, and a polymernetwork is formed in the liquid crystal layer of the liquid crystalcell. Pretilt of the liquid crystal molecules and an inclinationdirection of the liquid crystal molecules upon application of voltageare regulated by the polymer network.

According to the above arrangement, it is possible to provide a liquidcrystal display device by which a viewer can see an excellent image areaover a wide viewing angle and which provides for a high brightness.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more apparent from the followingdescription of the preferred embodiments, with reference to theaccompanying drawings, in which:

FIG. 1 is a diagrammatic view showing a liquid crystal display device ofthe first embodiment of the present invention;

FIG. 2 is a schematic cross-sectional view showing a liquid crystal cellof FIG. 1;

FIG. 3 is a schematic plan view showing the linear structures and liquidcrystal molecules of the liquid crystal cell of FIG. 2;

FIG. 4 is a view showing the portion A of FIG. 3 in detail;

FIG. 5 is a schematic cross-sectional view showing a variation of theliquid crystal cell of FIG. 2;

FIG. 6 is a schematic plan view of the liquid crystal cell of FIG. 5;

FIG. 7 is a schematic cross-sectional view showing a variation of theliquid crystal cell;

FIG. 8 is a schematic plan view showing the liquid crystal cell of FIG.7;

FIG. 9 is a view showing the portion of FIG. 8 in detail;

FIG. 10 is a schematic cross-sectional view showing a variation of theliquid crystal cell;

FIG. 11 is a schematic plan view showing the liquid crystal cell of FIG.9;

FIG. 12 is a schematic cross-sectional view showing a variation of theliquid crystal cell;

FIG. 13 is a schematic plan view showing the liquid crystal cell of FIG.11;

FIG. 14 is a view showing the portion A of FIG. 13 in detail;

FIG. 15A is a view showing the relation among polarizing axes of thefirst and second polarizers, optical axes of the first and secondretardation plates, and a direction of the liquid crystal layer, forexplaining the action of the retardation plate (λ/4);

FIG. 15B is a view showing the state of light passing through the firstpolarizer, the first retardation plate, the liquid crystal layer, thesecond retardation plate and the second polarizer;

FIGS. 16A to 16C are views showing the polarized light passing throughthe liquid crystal layer in the case where the retardation of the liquidcrystal layer is λ/2;

FIGS. 17A to 17C are views showing the polarized light passing throughthe liquid crystal layer and the retardation plate (λ/4) in the casewhere the retardation of the liquid crystal layer is λ/4;

FIG. 18 is a view showing an example of an image area of a conventionalliquid crystal display device in which the alignment division isconducted;

FIG. 19 is a view showing an example of an image area of the liquidcrystal display device in which the alignment division is conducted andthe first and second retardation plates are arranged;

FIG. 20A is a view showing the relation between the applied voltage andthe transmittance of the liquid crystal display device in which thealignment division is conducted according to the conventional manner andaccording to the present invention;

FIG. 20B is a view showing the relation between the transmittance andthe speed of response;

FIG. 21 is a view showing another example of the alignment division;

FIG. 22 is a view showing still another example of the alignmentdivision;

FIG. 23 is a view showing still another example of the alignmentdivision;

FIG. 24 is a view showing still another example of the alignmentdivision;

FIG. 25 is a graph showing the relation between the attainabletransmittance and the rise time in the case of alignment division shownin FIG. 24;

FIG. 26 is a view showing the relation between the cell thickness andthe transmittance in the case of the alignment division of the parallellinear structure type;

FIG. 27 is a view showing the relation between the cell thickness andthe transmittance in the case of the alignment division of the gratingtype;

FIG. 28 is a view showing the relation between the cell thickness andthe transmittance in the case of the alignment division of the fishbonetype;

FIG. 29 is a cross-sectional view showing another example of the liquidcrystal cell;

FIG. 30 is a plan view showing the liquid crystal cell of FIG. 29;

FIG. 31 is a view showing the liquid crystal cell having electricallyconductive linear structures of the liquid crystal display of the secondembodiment of the present invention;

FIG. 32 is a view showing a state of alignment of the liquid crystal inthe case of using the liquid crystal cell of FIG. 31;

FIG. 33 is a cross-sectional view showing another embodiment of theliquid crystal cell having electrically conductive linear structures;

FIG. 34 is a view showing a state of alignment of the liquid crystal inthe case of using the liquid crystal cell of FIG. 33;

FIG. 35 is a view showing another embodiment of the liquid crystal cellhaving electrically conductive linear structures;

FIG. 36 is a view showing a state of alignment of the liquid crystal inthe case where the liquid crystal cell of FIG. 35 is used;

FIGS. 37A to 37C are views showing the liquid crystal display device ofthe third embodiment of the present invention;

FIG. 38 is a view showing an example of the alignment division used inFIG. 37A;

FIGS. 39A to 39C are views showing a variation of the liquid crystaldisplay device shown in FIGS. 37A to 37C;

FIGS. 40A and 40B are views showing a variation of the liquid crystaldisplay device shown in FIGS. 37A and 37B;

FIGS. 41A to 41C are views showing a variation of the liquid crystaldisplay device shown in FIGS. 37A to 37C;

FIGS. 42A to 42C are views showing a variation of the liquid crystaldisplay device shown in FIGS. 37A to 37C;

FIGS. 43A to 43C are views showing a variation of the liquid crystaldisplay device shown in FIGS. 37A to 37C;

FIGS. 44A to 44C are views showing a variation of the liquid crystaldisplay device shown in FIGS. 37A to 37C;

FIGS. 45A to 45C are views showing a variation of the liquid crystaldisplay device shown in FIGS. 37A to 37C;

FIGS. 46A to 46C are views showing a variation of the liquid crystaldisplay device shown in FIGS. 37A to 37C;

FIGS. 47A to 47B are views showing a variation of the liquid crystaldisplay device shown in FIGS. 37A to 37C;

FIGS. 48A to 48C are views showing a variation of the liquid crystaldisplay device shown in FIGS. 37A to 37C;

FIGS. 49A to 49C are views showing a variation of the liquid crystaldisplay device shown in FIGS. 37A to 37C;

FIGS. 50A to 50C are views showing a variation of the liquid crystaldisplay device shown in FIGS. 37A to 37C;

FIGS. 51A to 51C are views showing a variation of the liquid crystaldisplay device shown in FIGS. 37A to 37C;

FIGS. 52A to 52C are views showing a variation of the liquid crystaldisplay device shown in FIGS. 37A to 37C;

FIGS. 53A and 53B are views showing a variation of the liquid crystaldisplay device shown in FIGS. 37A to 37B;

FIG. 54 is a view showing a variation of the liquid crystal displayshown in FIG. 37A;

FIG. 55 is a view showing a distribution of a quantity of transmissionlight on the front surface when the polarizers are set in a cross in theliquid crystal display shown in FIG. 54;

FIG. 56 is a view showing the liquid crystal display device of thefourth embodiment of the present invention;

FIGS. 57A and 57B are views for explaining the action of the specificdirection light scattering film shown in FIG. 56;

FIGS. 58A to 58C are views showing the alignment and the transmittanceof the liquid crystal molecules of the liquid crystal display device inwhich the alignment division is conducted;

FIG. 59 is a view showing a variation of the liquid crystal displaydevice shown in FIG. 56;

FIG. 60 is a view showing a variation of the liquid crystal displaydevice shown in FIG. 56;

FIG. 61 is a view showing the liquid crystal display device of the fifthembodiment of the present invention;

FIG. 62 is a view for explaining polarizing axes of the polarizers andoptical axes of the retardation plates of the liquid crystal displaydevice shown in FIG. 61;

FIG. 63 is a view showing a state of alignment of liquid crystalmolecules in the liquid crystal droplets shown in FIG. 63;

FIG. 64 is a view showing a display in the state of alignment of theliquid crystal molecules shown in FIG. 63;

FIG. 65 is a view showing a display of a conventional liquid crystaldisplay device;

FIG. 66 is a view showing the liquid crystal display of the sixthembodiment of the present invention;

FIG. 67 is view for explaining polarizing axes of the polarizers andoptical axes of the retardation plates of the liquid crystal displaydevice shown in FIG. 66;

FIG. 68 is a view showing a stabilization treatment of the liquidcrystal cell shown in FIG. 66;

FIG. 69 is a view showing the relation between the tone and the speed ofresponse in the case where the liquid crystal display device is used;and

FIGS. 70A to 70D are views showing a structure for the alignmentdivision of the liquid crystal display device shown in FIG. 66.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, embodiments of the present invention will beexplained below.

FIG. 1 is a view showing a liquid crystal display device of the firstembodiment of the present invention. The liquid crystal display device10 includes a liquid crystal cell 12. The liquid crystal cell 12includes a pair of substrates 14 and 16 having electrodes, and a liquidcrystal layer 18 arranged between the pair of substrates 14 and 16.Further, the liquid crystal display device 10 includes first and secondpolarizers 20 and 22 arranged on either side of the liquid crystal cell12, a first retardation plate 24 arranged between the liquid crystalcell 12 and the first polarizer 20, and a second retardation plate 26arranged between the liquid crystal cell 12 and the second polarizer 22.

Each of the first and second retardation plates 24 and 26 has an opticalaxis 24A, 26A in a plane parallel to the surfaces of substrates and aretardation of substantially λ/4. The optical axis 24A of the firstretardation plate 24 is perpendicular to the optical axis 26A of thesecond retardation plate 26. The polarizing axes 20A and 22A of thefirst and second polarizers 20 and 22 are arranged at an angle of 45°with respect to the optical axes 24A and 26A of the first and secondretardation plates 24 and 26.

The liquid crystal 18 of the liquid crystal cell 12 is of the verticalalignment type. The liquid crystal cell 12 is composed so that the stateof alignment of the liquid crystal molecules changes accompanying achange in the polar angle and a change in the azimuth upon applicationof voltage.

FIG. 2 is a schematic cross-sectional view showing the liquid crystalcell 12 of FIG. 1, and FIG. 3 is a schematic plan view showing thelinear structures and the liquid crystal molecules of the liquid crystalcell 12 of FIG. 2. The first substrate 14 has an electrode 28 and linearstructures (ribs) 30 formed on the electrode 28 and made of dielectricsubstance. The second substrate 16 has an electrode 32 and linearstructures (ribs) 34 formed on the electrode 32 and made of dielectricsubstance. Further, the first and second substrates 14 and 16respectively have vertical alignment films (not shown), and the liquidcrystal 18 has a negative anisotropy of the dielectric constant. One ofthe electrode 28 of the first substrate 14 and the electrode 34 of thesecond substrate 16 is a common electrode, and the other comprises pixelelectrodes formed together with TFTs. Further, the substrate having thecommon electrode has a color filter.

Only two linear structures 30 of the first substrate 14 are shown,however, it is possible to arrange a desired number of linear structuresin parallel to each other. Only one linear structure 34 of the secondsubstrate 16 is shown, however, it is possible to arrange a desirednumber of linear structures in parallel to each other. As shown in FIG.3, the linear structures 28 and 34 are alternately arranged so that theycan be parallel to each other when they are viewed on a plan view.

In the vertical alignment type liquid crystal display device, ingeneral, when voltage is not applied, liquid crystal molecules arealigned substantially perpendicularly to the substrate surfaces, andwhen voltage is applied, liquid crystal molecules are inclined withrespect to the substrate surfaces. When the linear structures 30 and 34are arranged, most of the liquid crystal molecules are alignedsubstantially perpendicularly to the substrate surfaces when voltage isnot applied, but the liquid crystal molecules 18X and 18Y located closeto the linear structures 30 and 34 tend to align perpendicularly to thewall surfaces of the linear structures 30 and 34 and are pretilted withrespect to the substrate surfaces. Therefore, when voltage is applied,the liquid crystal molecules 18X and 18Y located close to the linearstructures 30 and 34 are inclined in a predetermined direction accordingto the pretilt, so that most of the liquid crystal molecules areinclined depending on these liquid crystal molecules 18X and 18Y.

The direction of alignment of the liquid crystal molecules 18X locatedon one side of the linear structure 34 is opposite to the direction ofalignment of the liquid crystal molecules 18Y located on the other sideof the linear structure 34, so two regions in which the states ofalignment are different from each other are formed on either side of thelinear structures 34. This is also applied to the linear structures 30.Accordingly, even if rubbing is not conducted in this liquid crystaldisplay device 10, it is possible to realize the alignment division inthe same manner as in the case where pretilt is provided by rubbing. Bythe alignment division, it is possible to obtain an excellent viewingangle characteristic with high contrast in a wide viewing angle range.

That is, in a common liquid crystal display device, when a viewer seesan image area in the direction of the major axis of the inclined liquidcrystal molecules, the image area looks blackish, and when the viewersees the image area in the direction perpendicular to the major axis ofthe inclined liquid crystal molecules, the image area looks whitish. Inthe alignment division, there are liquid crystal molecules 18X, whichare inclined onto one side, and liquid crystal molecules 18Y, which areinclined onto the other side, in one pixel, so a whitish image and ablackish image are averaged in the image area, and accordingly, it ispossible for the viewer to see the image area with high contrast even ifthe image area is seen by a viewer in all oblique directions, in thesame manner as that of a case in which the viewer takes a front view ofthe image area. In this way, in the vertical alignment type liquidcrystal display device, the alignment division can realize an excellentviewing angle characteristic.

FIG. 4 is a view showing the portion A of FIG. 3 in detail. In theliquid crystal display device in which the alignment is divided in thisway, the state of alignment of most liquid crystal molecules in onepixel is substantially controlled according to the predeterminedstructures 30 and 34 when voltage is applied. That is, when voltage isapplied, the state of alignment of liquid crystal molecules changes froma state of alignment in which the liquid crystal molecules aresubstantially perpendicular to the substrate surfaces to a state ofalignment in which the liquid crystal molecules are inclined withrespect to the substrate surfaces, accompanying a change in the polarangle.

However, in some cases, the state of alignment of a portion of theliquid crystal molecules, upon application of voltage cannot becontrolled only by the predetermined structures 30 or 34. For example,as described above, the liquid crystal molecules 18X, which are inclinedonto one side with respect to the structure 30 or 34, and the liquidcrystal molecules 18Y, which are inclined onto the other side withrespect to the structure 30 or 34, must be continuously aligned to eachother. Therefore, the liquid crystal molecules 18P and 18Q, which arelocated intermediately between the liquid crystal molecules 18X and 18Yand on the structure 30 or 34, are aligned in parallel with thestructure 30 or 34. The liquid crystal molecules 18R and 18S adjacent tothe liquid crystal molecules 18P and 18Q are aligned, forming an angleof 45° with respect to the structure 30 or 34, for example.

The polarizers 20 and 22 are arranged in such a manner that thepolarizing axes 20A and 22A form an angle of 45° with respect to thedirector of the liquid crystal molecules upon application of voltage.The director of the liquid crystal molecules 18X, 18Y, 18P, and 18Qshown in FIG. 4 forms an angle of 45° with respect to the polarizingaxes 20A and 22A. However, the director of the liquid crystal molecules18R and 18S becomes parallel to the polarizing axes 20A and 22A.Therefore, black is displayed when white should be displayed, and blacklines represented by reference numeral 36 appear. That is, there is aproblem that brightness is deteriorated.

Further, since the direction of inclination of the liquid crystalmolecules 18R and 18S on the structure 30 or 34 cannot be controlled,part of the liquid crystal molecules 18R on the structure 30 or 34 andthe other part of the liquid crystal molecules 18S on the structure 30or 34 are aligned opposite to each other, immediately after voltage hasbeen applied. When a certain time passes after the application ofvoltage, the liquid crystal molecules 18R and 18S, which are alignedopposite to each other, are rotated in a plane of the sheet of FIG. 4(the state of alignment changes accompanying change in the azimuth) and,therefore, most of the liquid crystal molecules 18R and 18S on thestructure 30 or 34 are directed in the same direction and stabilized.Response time is determined at the point of time when the state ofalignment of the liquid crystal molecules 18R and 18A is stabilized.Accordingly, the change in the state of alignment accompanying thechange in the azimuth of the liquid crystal molecules 18R and 18S causesa problem in which the response of the liquid crystal display device isdeteriorated.

As described above, explanation has been given of the liquid crystaldisplay device having the structures 30 and 34. However, the sameexplanation may be made for a liquid crystal display device slits, whichwill be explained later, instead of the structures 30 and 34. Not onlythe state of alignment of the liquid crystal molecules 18R and 18S onthe structure 30 and 34 but also the state of alignment of the liquidcrystal molecules located close to the pixel edge is different from thestate of alignment of the liquid crystal molecules 18X and 18Y on eitherside of the structures 30 and 34, which could be a cause ofdeterioration of brightness.

The inventors have found that the problems of deterioration ofbrightness and deterioration of the response of the liquid crystaldisplay device with alignment division conducted as described above, canbe solved by arranging the first retardation plate (λ/4) 24 and thesecond retardation plate (λ/4) 26, as shown in FIG. 1.

FIGS. 15A and 15B are views for explaining the action of the retardationplate (λ/4) 24. In FIG. 15A, the polarizing axes 20A and 22A of thefirst and second polarizers 20 and 22 are perpendicular to each other,and the optical axes (slow axes) 24A and 26A of the first and secondretardation plates 24 and 26 and are perpendicular to each other. Thepolarizing axes 20A and 22A of the first and second polarizers 20 and 22and the optical axes (slow axes) 24A and 26A of the first and secondretardation plates 24 and 26 are arranged at an angle of 45° with eachother. In FIG. 15A, it is assumed that the optical axis 24A of the firstretardation plate 24 passes through the y-axis, and the optical axis 26Aof the second retardation plate 26 passes through the x-axis. The liquidcrystal layer 18 is provided with the director 18D as a whole. Thepolarizing axes 20A and 22 a of the first and second polarizers 20 and22 are arranged at an angle of 45° with respect to the director 18D ofthe liquid crystal layer 18.

FIG. 15B is a view showing the state of light passing through the firstpolarizer 20, the first retardation plate 24, the liquid crystal layer18, the second retardation plate 26 and the second polarizer 22. Lightmade incident to the first polarizer 20 becomes linearly polarizedlight; linear polarized light made incident to the first retardationplate 24 becomes counterclockwise circularly polarized light; circularlypolarized light made incident to the liquid crystal layer 18 becomesclockwise circularly polarized light; circularly polarized light madeincident to the second retardation plate 26 becomes linearly polarizedlight; and linearly polarized light made incident to the secondpolarizer 22 transmits through the second polarizer 22. In this case,retardation of the liquid crystal layer 18 is λ/2.

FIGS. 16A to 16C show the cases in which retardation of the liquidcrystal layer 18 is λ/2. FIG. 16A shows a case in which the director18D1 of the liquid crystal layer 18 is parallel to the y-axis, FIG. 16Bshows a case in which the director 18D2 of the liquid crystal layer 18is parallel to the x-axis, and FIG. 16C shows a case in which thedirector 18D3 of the liquid crystal layer 18 forms an angle of 45° withrespect to the x-axis. As can be seen in FIGS. 16A to 16C, all lighttransmitting through the liquid crystal layer 18 becomes circularpolarized light, irrespective of the direction of the director 18D ofthe liquid crystal layer 18. Accordingly, the transmittance of lightfinally transmitting through the second polarizer 22 does not dependupon the direction of the director 18D of the liquid crystal layer 18.

FIGS. 17A to 17C show the cases in which retardation of the liquidcrystal layer 18 is λ/4. FIG. 17A shows a case in which the director18D1 of the liquid crystal layer 18 is parallel to the y-axis, FIG. 17Bshows a case in which the director 18D2 of the liquid crystal layer 18is parallel to the x-axis, and FIG. 17C shows a case in which thedirector 18D3 of the liquid crystal layer 18 is arranged at an angle of45° with the x-axis. In FIG. 17A, in the case where retardation of theliquid crystal layer 18 is λ/4 and the director 18D1 of the liquidcrystal layer 18 is parallel to the y-axis, circular polarized lighttransmitting through the first retardation plate 24 is transmittedthrough the liquid crystal layer 18 and becomes linear polarized light.When this linear polarized light is transmitted through the secondretardation plate 26, it becomes circular polarized light, and acomponent (L22) of the circular polarized light in the direction ofy-axis is transmitted through the second polarizer 22.

In FIG. 17B, in the case where retardation of the liquid crystal layer18 is λ/4 and the director 18D2 of the liquid crystal layer 18 isparallel to the x-axis, circular polarized light transmitted through thefirst retardation plate 24 is transmitted through the liquid crystallayer 18 and becomes linear polarized light. When this linear polarizedlight is transmitted through the second retardation plate 26, it becomescircular polarized light, and a component (L22) of the circularpolarized light in the direction of y-axis is transmitted through thesecond polarizer 22.

In FIG. 17C, in the case where retardation of the liquid crystal layer18 is λ/4 and the director 18D3 of the liquid crystal layer 18 forms anangle of 45° with respect to the x-axis, circular polarized lighttransmitting through the first retardation plate 24 is transmittedthrough the liquid crystal layer 18 and becomes linear polarized light.When this linear polarized light is transmitted through the secondretardation plate 26, it becomes linear polarized light, and a component(L22) of the linear polarized light in the direction of y-axis istransmitted through the second polarizer 22.

In this way, the directions of polarization of polarized lighttransmitted through the second retardation plate 26 are different fromeach other, but the transmittance of light finally transmitted throughthe second polarizer 22 does not depend upon the direction of thedirector 18D of the liquid crystal layer 18.

In the case where retardation of the liquid crystal layer 18 isdifferent from λ/2 or λ/4, circular polarized light made incident to theliquid crystal layer 18 is transmitted through the liquid crystal layer18 and becomes elliptic polarized light. In this case too, thetransmittance of light transmitted through the second retardation plate26 and the second polarizer 22 does not depend upon the director 18D ofthe liquid crystal layer 18.

Accordingly, even when the liquid crystal cell 12 has minute portionscontaining the liquid crystal molecules 18X, 18Y, 18P, 18Q, 18R and 18S,the directors of which are different, as explained referring to FIG. 4,circular polarized light is transmitted through the liquid crystal layer18 and the second polarizer 22 in the same manner, without beingaffected by the change in the directors. Therefore, the deterioration ofbrightness can be prevented.

The fact that transmittance does not depend upon the director isadvantageous in the aspect of the response property. That is, when acertain time passes after the application of voltage, the liquid crystalmolecules 18R and 18S, the directions of which are opposite to eachother, are rotated in a plane of the sheet of FIG. 4 (the state ofalignment changes accompanying change in the azimuth), and the most ofthe liquid crystal molecules 18R and 18S on the structures 30 and 34 aredirected in the same direction and stabilized. Conventionally, theresponse is determined at a point of time when the state of alignment ofthe liquid crystal molecules 18R, 18S is stabilized. However, in thepresent invention, the intensity of the polarized light transmittedthrough the second polarizer 22 has already become constant at a pointof time when the liquid crystal molecules 18R and 18S on the structures30 and 34 are inclined in the opposite direction, so it is not necessaryto wait for change in the state of alignment accompanying change in theazimuth of the liquid crystal molecules 18R and 18S. Accordingly, theresponse time of the liquid crystal display device can be reduced.

FIG. 18 is a view showing an example of an image area of a conventionalliquid crystal display device with the alignment division. In FIG. 18,the black lines 36 appear, which have been explained referring to FIG.4. The black lines 36 can be a cause of the deterioration of brightness.

FIG. 19 is a view showing an example of the image area of the liquidcrystal display with the alignment division and the first and secondretardation plates 26. In FIG. 18, the black lines 36 appear which havebeen explained referring to FIG. 4. In FIG. 19, the black lines 36 ofFIG. 18 disappear.

FIG. 20A is a view showing the relation between the applied voltage andthe transmittance of the liquid crystal display device with thealignment division, of the prior art and the present invention. A curveplotted by black points relates to the conventional liquid crystaldisplay device, and a curve plotted by white points relates to theliquid crystal display device of the present invention. In both cases,the alignment division is realized by the combination of the linearstructures 30 and the slit 38 (shown in FIGS. 5 and 6). Thetransmittance is increased by 1.19 times at the voltage of 5.4 V. FIG.20B shows that the response speed is improved.

FIGS. 5 to 14 are views showing variations of the liquid crystal cell 12in which the alignment division shown in FIGS. 2 to 4 is conducted. Theliquid crystal cell 12 shown in FIGS. 5 to 14 can be adopted as theliquid crystal cell 12 shown in FIG. 1, and the liquid crystal cell 12shown in FIGS. 5 to 14 provide with the action which is explainedreferring to FIGS. 15 to 20.

In FIGS. 5 to 6, the first substrate 14 has the electrode 28 and linearstructures (ribs) 30 made of dielectric substance on the electrode 28.The second substrate 16 has the electrode 32 and slits 38 formed in theelectrode 32. The slit 38 includes a slit base section 38 a extending inthe same manner as that of the linear structure 34 shown in FIG. 3, andminute slit sections 38 b extending in the direction substantiallyperpendicular to the extending direction of the slit base section 38 a.The slit base section 38 a has the same action as that of the linearstructure 34 shown in FIG. 3. Since the minute slit sections 38 b arelocated in a portion forming a display domain, the influence of theelectric field strain is transmitted to the liquid crystal moleculesconstituting the display domain at high speed, and it is possible toimprove the performance of response of middle tone. Especially, when theshape of the minute slit sections 38 b is formed in a group of trianglesas shown in FIG. 6 so that the minute slit sections 38 b extend inparallel to the substrate surface, the speed of response can be highlyimproved.

In FIGS. 7 to 9, the first substrate 14 includes the electrode 28 andlinear structures (ribs) 30 made of dielectric substance on theelectrode 28, and the second substrate 16 includes the electrode 32 andlinear structures (ribs) 34 formed on the electrode 32. In this example,the linear structures 30 on the first substrate 14 are arranged in agrating pattern, and the linear structures 34 on the second substrate 16are arranged in a grating pattern but shifted from the linear structures30 on the first substrate 14. In this way, four liquid crystal alignmentregions including the liquid crystal molecules 18A, 18B, 18C, 18D areformed in a cross portion of the linear structures 30 and 34. In thiscase, since the directions of alignment of the liquid crystal molecules18A, 18B, 18C and 18D are different in the four liquid crystal alignmentregions, the effect obtained by the alignment division can be furtherenhanced. In this case, the polarizing axes 20A and 22A of the first andsecond polarizers 20 and 22 are arranged in parallel to the linearstructures 30 and 34, however, the liquid crystal molecules 18P and 18Qexist on the linear structures 30 and 34, which extend in parallel tothe linear structures 30 and 34 and are arranged in the oppositedirection to each other. The liquid crystal molecules 18P and 18Q wouldcause the black lines 36 and deteriorate the response. In the presentinvention, it is possible to improve the brightness and the response inthe same manner as that described before, by providing the first andsecond retardation plates 24 and 26.

In FIGS. 10 and 11, the first substrate 14 has the electrode 28, and nolinear structures or no slits. The second substrate 16 has the electrode32 and slits 38, which are formed in a fishbone pattern, in theelectrode 32. The slit 38 is composed of a slit base section 38 a andminute slit sections 38 b. The liquid crystal molecules 18A and 18B arealigned in the directions different from each other. The liquid crystalmolecules 18R are located on the slit base section 38 a.

In FIGS. 12 to 14, the first substrate 14 has the electrode 28 and nolinear structure or no slit. The second substrate 16 has the electrode32 and slits 38, which are formed in fishbone pattern, in the electrode32. The slit 38 is composed of a slit base section 38 a and minute slitsections 38 b. The end of the minute slit section 38 b becomes narrower.The liquid crystal molecules 18A and 18B are aligned in directionsdifferent from each other. The liquid crystal molecules 18R are locatedon the slit base section 38 a.

FIG. 21 is a view showing another example of the liquid crystal cell 12in which the alignment division is conducted. The liquid crystal cell 12is composed in such a manner that the liquid crystal layer 18 isarranged between the first substrate 14 and the second substrate 16. Thefirst and second retardation plates 24 and 26 and the first and secondpolarizers 20 and 22 are arranged on either side of the liquid crystalcell 12 (see FIG. 1). The first substrate 14 is a color filtersubstrate, and the second substrate 16 is a TFT substrate. The liquidcrystal cell 12 composes a liquid crystal panel of 15 inch XGA, and thepixel pitch is 297 μm.

Regarding one pixel electrode 19 (electrode 32), the linear structures30 of the first substrate 14 are formed in a bent shape, and the slits38 of the second substrate 16 are formed in a bent shape. In this case,the alignment division, in which the domain is divided into four, can berealized. The linear structures 30 are made of acrylic photosensitivematerial (for example, PC-335 manufactured by JSR), and the width of thelinear structure 30 is 10 μm, and the height of the linear structure 30is 1.2 μm. The width of the slit 38 is 10 μμm. The slits 38 are formedin the pixel electrode 19, and the slits 38 are discontinuously formedso that electric current can flow through the pixel electrode 19.

The distance between the linear structure 30 and the slit 38 is 25 μm.The thickness of the liquid crystal cell 12 is 4.64 μm. The first andsecond retardation plates (λ/4 plate) 24 and 26 are made of PC(polycarbonate, for example, NRF-RF01A manufactured by Nitto Denko Co.).In this case, the retardation is 140 nm. However, it is possible to usea retardation plate made of other material (for example, arton filmmanufactured by JSR). The first and second polarizers 20 and 22 are madeof G1220DU manufactured by Nitto Denko Co.

In the case where the polarizers 20 and 22 are arranged in a cross or aplus sign arrangement (the polarizing axes 20A and 22A are arrangedvertically and horizontally in the sheet of FIG. 21, and in thisexample, the polarizing axes 20A and 22A form an angle of 45° withrespect to the main liquid crystal director), the white transmittance is6.43%. In the same arrangement, when the polarizers 20 and 22 arearranged in a 45° arrangement (for example, the polarizing axes 20A and22A form an angle of 45° with respect to the vertical and the horizontalin FIG. 21), the white transmittance is 6.58%. In this connection, thearrangement of the polarizers 20 and 22 is not limited to the plus signarrangement and the 45° arrangement, and the polarizers 20 and 22 can bearbitrarily arranged. On the other hand, in the case of a conventionalliquid crystal display device having no retardation plate 24 or 26, thewhite transmittance is 5.05% in the case of plus sign arrangement.

In the embodiment, the gap distance between the linear structure 30 andthe slit 38 is 25 μm, but this distance can be changed. In the case of aconventional liquid crystal display, with alignment division and withoutfirst and second retardation plates (λ/4 plate) 24 and 26, the followingproblem may be encountered; the response speed is increased but thetransmittance is lowered if the gap distance is reduced, and thetransmittance is increased but the response speed is decreased, if thegap distance is increased. This problem is caused by change in azimuthof alignment of the liquid crystal molecules or decrease ordeterioration of the transmittance due to the change in the azimuth ofalignment of the liquid crystal molecules. In the present invention,since the transmittance does not depend upon the azimuth of alignmentthe liquid crystal molecules, the influence of the decrease of thetransmittance or the decrease of the response speed due to the change inthe gap distance is not so much as compared with the conventionalarrangement. Therefore, it is possible to apply a liquid crystal displaydevice with a greater gap distance or a smaller gap distance accordingto the use for an animated cartoon or the use for a brighter display,which cannot be conventionally applied.

FIG. 22 is a view showing another embodiment of the liquid crystal cellwith the alignment division. Regarding one pixel electrode 19, thelinear structures 30 of the first substrate 14 are formed in the bentshape, and the slits 38 of the second substrate 16 are formed in thebent shape. The slit 38 is formed in the same manner as that shown inFIG. 6. In this case, the alignment division in which the domain isdivided into four, is realized. The width of the linear structure 30 andthe slit 38 is 10 μm. The pitch of the minute slit section is 6 μm, andthe length of the minute slit section is 15 μm.

The liquid crystal cell 12 is manufactured under substantially the sameconditions as that of the liquid crystal cell shown in FIG. 21 exceptfor that the thickness of the liquid crystal cell 12 is 4.26 μm. In thecase where the polarizers 20 and 22 are arranged in the plus signarrangement, the white transmittance is 5.74%. In the case where thepolarizers 20 and 22 are arranged in the 45° arrangement, the whitetransmittance is 5.88%. On the other hand, in the case of a conventionalliquid crystal display device having no retardation plates 24 and 26,when the polarizers 20 and 22 are arranged in the plus sign arrangement,the white transmittance is 4.47%. In this example, since the cellthickness is smaller than that of the example shown in FIG. 21, theretardation of the liquid crystal layer 18 is decreased and an absolutevalue of the transmittance is a little low, but the effect ofimprovement by providing the retardation plates is as high as that ofthe example shown in FIG. 21.

FIG. 23 is a view showing another embodiment of the liquid crystal cellwith the alignment division. The first substrate 14 has the linearstructures 30, and the second substrate 16 has slits 38. The linearstructures 30 and the slits 38 are arranged in the grating pattern inthe same manner as that of the linear structures 30 and 34 of the liquidcrystal cell 12 shown in FIG. 9. The width of the linear structure 30 is8 μm, and the height of the linear structure 30 is 0.75 μm. The width ofthe slit 38 is 8 μm. The thickness of the cell is 4.02 μm. In the casewhere the polarizers 20 and 22 are arranged in the plus signarrangement, the white transmittance is 5.86%. In the case where thepolarizers 20 and 22 are arranged in the 45° arrangement, the whitetransmittance is 5.78%. On the other hand, in the case of a conventionalliquid crystal display device having no retardation plates 24 and 26,when the polarizers 20 and 22 are arranged in the plus sign arrangement,the white transmittance is 4.48%.

FIG. 24 is a view showing another embodiment of the liquid crystal cellwith the alignment division. This example includes two fishbone patternsof slits 38A and 38B, which are similar to the fishbone pattern of slits38 shown in FIG. 11. The cell thickness is 3.86 μm. Other conditions arethe same as those of the example shown in FIG. 21. In the case where thepolarizers 20 and 22 are arranged in the plus sign arrangement, thewhite transmittance is 6.26%. In the same structure, in the case wherethe polarizers 20 and 22 are arranged in the 45° arrangement, the whitetransmittance is 6.06%. On the other hand, in the case of a conventionalliquid crystal display device having no retardation plates 24 and 26,when the polarizers 20 and 22 are arranged in the plus sign arrangement,the white transmittance is 5.12%.

FIG. 25 is a view showing the relation between the attainabletransmittance and the rise time in the case of alignment division shownin FIG. 24. The curve plotted by black triangles shows a case in whichthe alignment division shown in FIG. 24 is adopted but no retardationplates are provided, and the curve plotted by white triangles shows acase in which the alignment division shown in FIG. 24 is adopted andretardation plates are provided. Conventionally, in this system, theresponse time in all gradation including the middle tones is severalhundred ms. Therefore, this system is not suitable for a liquid crystaldisplay device applied to a liquid crystal monitor, for example.However, when the present invention is applied to this system, a highspeed response is realized as follows. The response time from black towhite is 20 ms, and even the response time from black to the middle tome(25%) is 90 ms. Therefore, this system can be applied to a liquidcrystal device such as a liquid crystal monitor.

FIGS. 26 to 28 are views showing the relation between the cell thicknessand the transmittance. FIG. 26 shows the relation between the cellthickness and the transmittance in the case of the alignment divisionrealized by parallel linear structures (for example, FIG. 21). FIG. 27shows the relation between the cell thickness and the transmittance inthe case of the alignment division realized by the grating pattern,shown, for example, in FIG. 23. FIG. 28 shows the relation between thecell thickness and the transmittance in the case of the alignmentdivision realized by fishbone pattern, shown, for example, in FIG. 24.

In these views, the curve plotted by squares shows a case in which noretardation plates (λ/4) are provided and the polarizers are arranged inthe plus sign arrangement, the curve plotted by triangles shows a casein which retardation plates (λ/4) are provided and the polarizers arearranged in the plus sign arrangement, and the curve plotted by blackcircles shows a case in which retardation plates (λ/4) are provided andthe polarizers are arranged in the 45° arrangement.

In curve plotted by squares shown in FIG. 26, when the cell thickness is4.2 μm, the transmittance is 4.4%, which is the same as that of a liquidcrystal display device which is used by the present applicant. Accordingto the curves plotted by triangles and black circles, when the cellthickness is 4.2 μm, the transmittance is 5.8%. Further, according tothe curve plotted by black circles shown in FIG. 27, when the cellthickness is 4.2 μm, the transmittance is 6.2%. According to the curveplotted by black circles shown in FIG. 28, when the cell thickness is4.2 μm, the transmittance is 6.9%. As described above, according to thepresent invention described above, it is possible to enhance thetransmittance.

FIG. 29 is a cross-sectional view showing another embodiment of theliquid crystal cell with the alignment division. FIG. 30 is a plan viewshowing the liquid crystal cell of FIG. 29. The liquid crystal cell 12includes a pair of substrates 14 and 16 having electrodes and a liquidcrystal layer 18 arranged between the pair of substrates 14 and 16. Thisliquid crystal cell 12 is used together with the first and secondpolarizers 20 and 22 and the first and second retardation plates 24 and26 shown in FIG. 1. In this embodiment, the liquid crystal layer 18 isnot limited to the vertical alignment, but the liquid crystal layer 18of the horizontal alignment type may be used. However, the liquidcrystal layer 18 is composed in such a manner that the state ofalignment of the liquid crystal molecules 18H changes accompanying achange in the polar angle and a change in the azimuth angle uponapplication of voltage. It is not necessary for the substrates 14 and 16to have the linear structures (ribs) 30 and 34 and the slits 38 forcontrolling the alignment.

FIG. 31 is a view showing a liquid crystal display device of the secondembodiment of the present invention, with a liquid crystal cell havingelectrically conductive linear structures. The liquid crystal displaydevice 10 includes a liquid crystal cell 12 in which the liquid crystallayer 18 is arranged between the first and second substrates 14 and 16,first and second polarizers 20 and 22, and first and second retardationplates 24 and 26 (see FIG. 1).

The first substrate 14 has linear structures 30, and the secondsubstrate 16 has linear structures 34. The linear structures 30 and 34are alternately arranged in parallel with each other as explainedbefore, for example, as shown in FIG. 3. The linear structures 30 and 34may be arranged in a grating pattern or a fishbone shape.

The linear structures 30 and 34 are electrically conductive structures.In FIG. 31, the linear structures 30 are made of the same metallicmaterial as that of the electrode 28 of the first substrate 14, and thelinear structures 34 are made of the same metallic material as that ofthe electrode 32 of the second substrate 16. For example, linearprotrusions are formed on the substrate in advance before the electrode28 and 32 are formed, and the electrode 28 and 32 are formed on thesubstrate by ITO. Alternatively, the linear structures 30 and 34 areformed on the electrode 28 and 32 by an electrically conductive resinsuch as a resin in which conductive grains of carbon are mixed. Theheight of the linear structures 30 and 34 is 0.1 μm to half of the cellthickness. As an example, the height of the linear structures 30 and 34is 1.5 μm. A vertical alignment film is coated on the electrode 32 andthe linear structures 30 and 34.

In the embodiments described above, the linear structures 30 and 34 aremade of dielectric substance. In the case where the linear structures 30and 34 are made of dielectric substance, part of voltage suppliedbetween the electrodes 28 and 29 is absorbed by the dielectricsubstance, so that voltage applied to the liquid crystal is lowered.Therefore, the liquid crystal molecules are insufficiently inclined whenvoltage is applied, and the transmittance is lowered. In thisembodiment, since the linear structures 30 and 34 are electricallyconductive, part of voltage supplied between the electrodes 28 and 32 isnot absorbed, and voltage applied to the liquid crystal is not lowered,and thus the liquid crystal molecules are sufficiently inclined whenvoltage is applied, and the transmittance is not lowered.

FIG. 32 is a view showing a state of alignment of the liquid crystal inthe case where the liquid crystal cell shown in FIG. 31 is used. It canbe understood that the liquid crystal molecules are sufficientlyinclined or lie when voltage is applied.

FIG. 33 is a view showing another embodiment of the liquid crystal cellhaving electrically conductive linear structures. The first substrate 14has linear structures 30 and slits 38. The second substrate 16 has nolinear structure or no slit. However, it is possible to adopt anarrangement in which the first substrate 14 has linear structures 30 andthe second substrate 16 has slits 38.

FIG. 34 is a view showing a state of alignment of the liquid crystal inthe case where the liquid crystal cell shown in FIG. 33 is used. It canbe understood that when voltage is applied, the liquid crystal moleculeslocated close to the slit 38 are not sufficiently inclined, but theliquid crystal molecules located close to the linear structure 30 aresufficiently inclined. When the arrangement shown in FIG. 33 is adopted,it is possible to realize excellent alignment division, and further thetransmittance can be enhanced.

FIG. 35 is a view showing another embodiment of the liquid crystal cellhaving electrically conductive linear structures. The first substratehas linear structures 30M and linear structures 30D, and the secondsubstrate 16 has no linear structure or no slit. The linear structures30M are electrically conductive, and the linear structures 30D aredielectric. In the case where the linear structures 30M are arranged atlong intervals, the linear structure 30D is arranged between the linearstructures 30M.

FIG. 36 is a view showing a state of alignment of the liquid crystal inthe case where the liquid crystal cell shown in FIG. 35 is used. It canbe understood that when voltage is applied, the liquid crystal moleculeslocated close to the linear structure 30D are not sufficiently inclined,but the liquid crystal molecules located close to the linear structure30M are sufficiently inclined. When the arrangement shown in FIG. 35 isadopted, it is possible to attain excellent alignment division, andfurther the transmittance can be enhanced.

FIGS. 37A to 37C are views showing a liquid crystal display device ofthe third embodiment of the present invention. FIG. 37A shows anarrangement of the liquid crystal display device, FIG. 37B shows thecontrast of the display when a viewer takes an oblique view of the imagearea, and FIG. 37C shows the relation between applied voltage and thequantity of transmitting light. As shown in FIG. 37A, the liquid crystaldisplay device 10 includes a liquid crystal cell 12, first and secondpolarizers 20 and 22, and first and second retardation plates 24 and 26.

The first and second retardation plates 24 and 26 respectively have theoptical axes 24A and 26A in a plane parallel to the surfaces of thesubstrates, and the retardation between the optical axes 24A and 26A isapproximately λ/4. The optical axis 24A of the first retardation plate24 is perpendicular to the optical axis 26A of the second retardationplate 26. The polarizing axes 29A and 22A of the first and secondpolarizers 20 and 22 are respectively arranged at an angle of 45° withrespect to the optical axes 24A and 26A of the first and secondretardation plates 24 and 26. The retardation in the plane of the firstand second retardation plates 24 and 26 is not less than 120 nm and notmore than 160 nm. It is preferable that the retardation in the plane ofthe first and second retardation plates 24 and 26 is not less than 130nm and not more than 145 nm.

The first polarizer 20 comprises a polarizing layer (for example,PVA+iodine) 22 p, and protective layers (for example, TAC; triacetylcellulose) 20 q and 20 r which cover both sides of the polarizing layer20 p. In the same manner, the second polarizer 22 comprises a polarizinglayer (for example, PVA+iodine) 22 p; and protective layers (forexample, TAC; triacetyl cellulose) 22 q and 22 r which cover both sidesof the polarizing layer 22 p.

The liquid crystal cell 12 comprises the liquid crystal layer 18arranged between the first and second substrates 14 and 16, as shown inFIG. 1. Also, the liquid crystal layer 18 comprises the liquid crystalof vertical alignment type. The liquid crystal cell includes structuresor slits provided on or in the electrode of at least one of thesubstrates. The state of alignment of the liquid crystal moleculeslocated on one side of the structure or slit is different from the stateof alignment of the liquid crystal molecules located on the other sideof the structure or slit. Concerning the structures or slits, all thestructures and slits explained before can be used.

FIG. 38 is a view showing an example of the alignment division conductedin FIG. 37A. The alignment division includes bent linear structures 30provided on the electrode of the first substrate 14, and bent linearslits 38 provided in the electrode of the first substrate 14. In thisalignment division, the liquid crystal molecules are aligned in fourdirections, as shown by the arrows 18C, 18D, 18E and 18F. That is, thealignment division in which one pixel is divided into four domains isrealized. In FIG. 38, gate bus lines 40, data bus lines 42, TFTs 44 andsubsidiary capacity electrode 46 are shown. The polarizers 20 and 22 arearranged in the plus sign arrangement.

In the arrangement shown in FIGS. 37A and 38, the contrast is shown inFIG. 37B, in which the azimuth at which the highest contrast is obtainedis rotated counterclockwise by about 30° from the vertical and thehorizontal. Concerning the viewing angle characteristic, the range ofoblique viewing angle at which the contrast is not less than 10° is notless than 40°.

FIGS. 39A to 39C are views showing a variation of the liquid crystaldisplay device shown in FIGS. 37A to 37C. FIG. 39A shows the arrangementof the LCD, FIG. 39B shows the contrast, and FIG. 39C shows the T-Vcharacteristic, corresponding to FIGS. 37A to 37C. This is also appliedto the following variations of FIGS. 40A to 53B. The liquid crystaldisplay device 10 shown in FIG. 39A is arranged in the substantiallysame manner as that of the liquid crystal display device shown in FIG.37A, but a compensation film (for example, a TAC film) 48 having anegative retardation is arranged or laminated between the firstretardation plate (λ/4) 24 and the liquid crystal cell 12, and acompensation film (for example, a TAC film) 50 having a negativeretardation is arranged or laminated between the second retardationplate (λ/4) and the liquid crystal cell 12, and a compensation films 48and 50 are laminated, a positive retardation of the liquid crystal layer18 is compensated for, and a range in which the contrast is not lessthan 5 is extended as shown in FIG. 39B. The viewing angle range inwhich the contrast is not less than 10 can be extended, and the contrastis kept to be not less than 10 even if the oblique viewing angleincreased to 50°. However, in the T-V characteristic shown in FIG. 39C,the brightness tends to decrease when voltage is increased. As a result,the reversal of gradation tends to occur.

FIGS. 40A and 40B are views showing a case in which the compensationfilms 48 and 50 having the positions of a negative retardation are notclose to the liquid crystal cell 12 but distant from the liquid crystalcell 12. Although the compensation films 48 and 50 are added, the degreeof improvement in the viewing angle characteristic is inferior to thatof FIGS. 39A to 39C. Due to the foregoing, it is found that it ispreferable to arrange the compensation films 48 and 50 having a negativeretardation close to the liquid crystal cell 12.

FIGS. 41A to 41C are views showing a variation of the liquid crystaldisplay device shown in FIGS. 37A to 37C. The setting angles of thepolarizers 20 and 22 are changed from the values shown in FIG. 37A. Thepolarizers 20 and 22 are set at azimuth angles of 45° and 135°, and theλ/4 plates 24 and 26 are arranged in the plus sign arrangement. In thiscase, contrast curves show that the range, in which the contrast is notless than 5, as shown in FIG. 41B, is extended as compared with theembodiment of FIG. 37B. According to T-V characteristic, it can beunderstood that the decrease of the brightness on the high voltage sideis not so much and the gradation characteristic is excellent, as shownin FIG. 41C.

FIGS. 42A to 42C show a variation of the liquid crystal display deviceshown in FIGS. 37A to 37C. In this arrangement, TAC films, as negativecompensation films, 48 and 50 are arranged between the liquid crystalcell 12 and the λ/4 plates 24 and 26, respectively. Due to theforegoing, it is possible to extend a viewing angle range in which thehigh contrast can be obtained (refer to data shown in FIGS. 41B and42B). However, in the T-V characteristic, the brightness is lowered onthe high voltage side, and a reversal of gradation tends to occur.

FIGS. 43A to 43B are views showing a variation of the liquid crystaldisplay device shown in FIGS. 37A to 37C. In this arrangement, theangles of the polarizers 20 and 22 are optimized, so that the viewingangle azimuth at which the contrast becomes maximum is set at thevertical and the horizontal. In this case, calculation is made supposingthat the retardation plates (λ/4) 24 and 26 are perfect uniaxial films.The direction of the absorbing axis 22A of the polarizer 22 on theincident side is set at an azimuth angle of 145° and the arrangement ofCross-Nicol arrangement is adopted. The direction of the slow axis 26Aof the retardation plate 26 adjacent to the polarizer 22 is set at anazimuth angle of 10°, that is, the direction of the slow axis 26A of theretardation plate 26 adjacent to the polarizer 22 is set at an angle of45° with respect to the absorbing axis 22A of the polarizer 22 on theincident side. The slow axis 24A of the retardation plate 24 of the pairis set at an azimuth angle of 100°, that is, the slow axis 24A of theretardation plate 24 is set so that the slow axes 24A and 26A of thepair of retardation plates 24 and 26 are perpendicular to each other. Inthis arrangement, no compensation films are provided.

FIGS. 44A to 44C are views showing a variation of the liquid crystaldisplay device shown in FIGS. 43A to 43C. In this arrangement, theangles formed between the polarizers 20 and 22 and the retardationplates 24 and 26 are fixed with respect to those of FIGS. 43A to 43C,and TAC films as negative compensation layers 48 and 50 are laminatedbetween the liquid crystal cell 12 and the retardation plates 24 and 26,respectively. Due to the foregoing, the viewing angle range is extendedas compared with the viewing angle range shown in FIGS. 43A to 43C. Theretardation plate 24(26) and 48(50) can be one plate, or the plate24(26) can have the negative retardation whose value is almost equal tothe addition of the negative retardation of plate 24(26) and that ofplate 48(50).

In the foregoing embodiments, an explanation was made regarding thealignment division in which one pixel is divided into four domains.Explanation is next made regarding the alignment division in which onepixel is divided into two domains. Concerning the two-divided alignmentdivision, the alignment is divided into two, that is, vertically upperand lower portions. Upon the application of voltage to the liquidcrystal molecules, the liquid crystal molecules of the upper half of thepixel are inclined to the lower azimuth, and the liquid crystalmolecules of the lower half of the pixel are inclined to the upperazimuth.

FIGS. 45A to 45C are views showing a variation of the liquid crystaldisplay device shown in FIGS. 37A to 37C. The polarizers 20 and 22 areset in the cross, and the retardation plates 24 and 26 are respectivelyset at the azimuth angles of 45° and 135°.

FIGS. 46A to 46C are views showing a variation of the liquid crystaldisplay device shown in FIGS. 45A to 45C. FIGS. 37A to 37C show the caseof the four-divided alignment division. On the other hand, FIGS. 46A to46C show the case of the two-divided alignment division. Arrangements ofthe polarizers and films are the same as those shown in FIG. 37A. TACfilms as negative compensation layers 48 and 50 are laminated betweenthe liquid crystal cell 12 and the retardation plates 24 and 26,respectively.

FIGS. 47A and 47B are views showing a variation of the liquid crystaldisplay device shown in FIGS. 37A to 37B. In this arrangement, thesetting angles of the polarizers 20 and 22 and the retardation plates 24and 26 are changed, so that the viewing angle characteristic is made tobe symmetrical with respect to the vertical and the horizontaldirections. The absorbing axis 22A of the polarizer 22 on the incidentside is set at an azimuth angle of 120°, the slow axis 26A of theretardation plate 26 close to the polarizer 22 is set at an azimuthangle of 75°, the slow axis 24A of the retardation plate 24 of the pairis set at an azimuth angle of −15°, and the absorbing axis 20A of thepolarizer 20 on the emergent side is set at an azimuth angle of 30°.

FIGS. 48A to 48C are views showing a variation of the liquid crystaldisplay device shown in FIGS. 47A and 47B. TAC films, as negativecompensation layers, 48 and 50 are laminated between the liquid crystalcell 12 and the retardation plates 24 and 26, respectively. Theabsorbing axis 22A of the polarizer 22 on the incident side is set at anazimuth angle of 155°, the slow axis 26A of the retardation plate 26close to it is set at an azimuth angle of 20°, the slow axis 24A of theretardation plate 24 of the pair is set at an azimuth angle of 110°, andthe absorbing axis 20A of the polarizer 20 on the emergent side is setat an azimuth angle of 65°. Due to the foregoing, the symmetry is lost,however, it is possible to realize a wide range of contrast.

FIGS. 49A to 49C are views showing a variation of the liquid crystaldisplay device shown in FIGS. 37A to 37C. This arrangement is devisedsuch that the retardation of the liquid crystal layer 18 is completelycanceled, and the viewing angle range of the polarizers 20 and 22 ismaximized and, further, leakage of light caused by the retardationplates 24 and 26 is minimized. The arrangement is explained from thepolarizer 22 on the backlight side. An angle of the absorbing axis 22Aof the polarizer 22 is set at an azimuth angle of 135°, the slow axis26A of the λ/4 plate 26 is then set at an azimuth angle of 0°, andaligning directions of the liquid crystal cell 12 of the four-dividedalignment division are set at azimuth angles of 45°, 135°, 225° and315°. Next, in order to completely cancel a birefringence of the liquidcrystal layer 18 which is vertically aligned, an optical layer 52 havingindices of refraction in the form of a profile of a sitting cushion isset (Δnd is the same as that of the liquid crystal layer), the slow axis24A of the λ/4 plate 24 is then set at an azimuth angle of 90°, auniaxial optical layer 54 having a slow axis perpendicular to thesubstrates (expressed as a Rugby ball type in the drawing) is set. Next,the film 56, which is a uniaxial film and the retardation of which is140 nm, is set in such a manner that the slow axis 56A is set at anazimuth angle of 135°, and the polarizer 20 is then set in such a mannerthat the absorbing axis 20A is set at an azimuth angle of 45°. In thiscase, the symmetric characteristic with respect to the vertical andhorizontal directions is obtained, and further even in the azimuth ofoblique angle of 45°, the range of the oblique viewing angle in whichthe contrast is not less than 10 is 50°. In this case, it is preferablethat the retardation of the optical layer 52, the profile of which islike sitting cushion, is the same as the retardation of the liquidcrystal layer 18. When the retardation is set in the range of ±10%, itis possible to extend the range of good contrast.

FIGS. 50A to 50C are views showing a variation of the liquid crystaldisplay device shown in FIGS. 49A to 49C. This variation is differentfrom the embodiment shown in FIG. 49A at the setting angles of thepolarizers 20 and 24. The arrangement will be explained from thepolarizer 22 on the backlight side. The absorbing axis 22A of thepolarizer 22 is set at an azimuth angle of 0°, the slow axis 26A of theλ/4 plate 26 is set at an azimuth angle of 45°, and the alignmentdirections of the four-divided alignment division of the liquid crystalcell 12 are set at azimuth angles of 45°, 135°, 225° and 315°. Next, inorder to completely cancel birefringence of the liquid crystal layerwhich is vertically aligned, the optical layer 52 having indices ofrefraction in a profile of sitting cushion is set (Δnd is the same asthat of the liquid crystal layer). Next, the slow axis 24A of the λ/4plate 24 is set at an azimuth angle of 135°. Next, the uniaxial opticallayer 54 is set, the profile of which is expressed as a Rugby ball typein the drawing, the slow axis of which is perpendicular to thesubstrate. Next, a film 56, which is a uniaxial film and the retardationof which is 140 nm, is set in such a manner that the slow axis 56A isset at an azimuth angle of 0°. Then, the polarizer 20 is set in such amanner that the absorbing axis 20A is set at an azimuth angle of 90°. Inthis case, the azimuth at which the contrast is highest is displaced andis 45° with respect to the vertical and the horizontal, but the obliqueviewing angle at which the contrast becomes 5 is 75° at the worst, andit is possible to realize a wide viewing angle range.

FIGS. 51A to 51C are views showing a variation of the liquid crystaldisplay device shown in FIGS. 37A to 37C. In the embodiment shown inFIGS. 49A to 49C, the alignment is divided into four, however, in thisembodiment, the alignment is divided into two. Essentially, with respectto the embodiment shown in FIGS. 49A to 49C, this embodiment is composedin such a manner that the alignment directions are 90° and 270°, thatis, the alignment is divided into two, and the arrangements of thepolarizers 20 and 22, the films 52, 54 and 56 for improving the viewingangle and the λ/4 plates are the same as those shown in FIGS. 49A to49C. When the viewing angle characteristic is checked, concerning theviewing angle characteristic of the ratio of contrast, thecharacteristic of this embodiment is superior to that of the embodimentshown in FIGS. 49A to 49C. On the other hand, when the T-Vcharacteristic is checked, the undulation of the T-V characteristic uponthe application of voltage becomes larger than that of FIG. 49C.Therefore, it can be understood that the viewing angle characteristic inthe case of displaying a middle tone is inferior but it can beconsidered that the arrangement of two-divided alignment division can beeasily manufactured as compared with the arrangement of four-dividedalignment division.

FIGS. 52A to 52C are views showing a variation of the liquid crystaldisplay device shown in FIGS. 37A to 37C. With respect to the embodimentshown in FIGS. 50A to 50C, in this embodiment, the setting angles of thepolarizers 20 and 22 and the compensation films 52, 54 and 56 are notchanged, and the alignment of the liquid crystal cell 12 is divided intotwo, in which the alignment azimuth angles are set at 90° and 270°.

FIGS. 53A and 53B are views showing a variation of the liquid crystaldisplay device shown in FIGS. 37A to 37C. In the embodiment describedbefore, a uniaxial oriented film, especially an optically uniaxial film,is used for the λ/4 plates 24 and 26. On the other hand, in thisembodiment, a film, the negative retardation (=(nx+ny)/2−nz) of which iszero, is used for the λ/4 plates 24 and 26. When the viewing anglecharacteristic (shown in FIG. 53B) of the ratio of contrast in this caseis checked, a line of the contrast 10 cannot be seen, and an excellentviewing angle characteristic can be realized in the range of an azimuthoblique angle of 80°. Concerning the film, the negative retardation ofwhich is 0, it is possible to use NZ Film manufactured by Nitto DenkoCo. and SZ Film manufactured by Sumitomo Kagaku Co. which are on themarket. Concerning the negative retardation (=(nx+ny)/2−nz), when it isset at 0±20 nm, it is possible to realize an especially wide viewingangle. Further, while the absorbing axis of the polarizer on one sideand the slow axis of the phase film 56 are made to be perpendicular toeach other, the phase film 56 is set close to the polarizer 20.Concerning the value of the retardation on the face of the phase film56, when the phase film 56 is arranged close to both of the pair ofpolarizers, the value is set in the range not less than 25 nm and notmore than 70 nm. When the phase film 56 is arranged close to only thepolarizer on one side, the value is set in the range not less than 60 nmand not more than 160 nm (in this example, 140 nm). Further, the film 52having a positive optical anisotropy in the vertical direction is put onthe substrate, and the position is set between the λ/4 plate 26 and thepolarizer 22. In this case, a value of the retardation is set in therange not less than 80 nm and not more than 300 nm. The value ispreferably set at 90 nm±10 nm. In this case, it is possible to realizean especially wide viewing angle as shown in FIG. 53B. The retardationof plate 54[={(nx+ny)/z−nz}×d] is almost equal to the retardation ofvertically aligned 2C cell 12 (Δn·d).

FIG. 54 is a view showing the relation between the alignment regulatingdirections to realize the four-divided alignment division and thealignment directions of liquid crystal molecules realized at the time.The solid line arrows 18I and 18J show azimuths to which the liquidcrystal molecules on the TFT substrate side are tilted down, and thedotted line arrows 18K and 18L show azimuths to which the liquid crystalmolecules on the CF substrate side are tilted down. By these alignmentregulating means, the action to tilt the liquid crystal molecules isexerted as shown by the bold arrows 18C, 18D, 18E and 18F. The thusobtained result of regulating the alignment azimuth is shown by the boldarrow 18M. In this case, the characteristic thing is that the directionsof the bold arrows 18C, 18D, 18E and 18F do not coincide with thedirection of the bold arrow 18M. In this case, in the intermediateregion of the alignment regulating azimuths shown by the bold arrows18C, 18D, 18E and 18F, the alignment of the liquid crystal molecules isdirected to the azimuth so that the intermediate region of the alignmentregulating azimuth can be equally divided into two. Therefore, when theentire pixel is viewed, it is tilted toward the center of the pixel likethe petals of tulip, that is, it is tilted toward the center of thepixel as if a flower of tulip were in bloom being directed outside.

FIG. 55 is a view showing a distribution of a quantity of transmissionlight on the front face when the polarizers are set being formed into across. As shown in the view, a black cross region exists at the centerof the pixel. Therefore, it is impossible to obtain a bright display.When the λ/4 plates are set on both sides of the liquid crystal layer inthis case, it is possible to realize a bright display.

Concerning the method of regulating the alignment shown in FIG. 54, theoptical alignment method and the rubbing method were used. As explainedabove, when the present invention is applied, it is possible to realizea bright display and it is also possible to realize a liquid crystaldisplay device having a wide viewing angle.

FIG. 56 is a view showing a liquid crystal display device of the fourthembodiment of the present invention. FIGS. 57A and 57B are views forexplaining an action of the specific direction light scattering filmshown in FIG. 56. FIGS. 58A to 58C are views showing the alignment ofliquid crystal molecules and the transmittance of the liquid crystaldisplay device in which the alignment is divided. In FIG. 56, the liquidcrystal display device 10 includes a liquid crystal cell 12, first andsecond polarizers 20 and 22, a specific direction light scattering film60, and a viewing angle improving film 62. The polarizers 20 and 22 arecomposed of polarizing layers 20 p and 22 p and protective layers 20 q,20 r, 22 q and 22 r, as shown in FIG. 39A. The protective layer 20 rshown in FIG. 56 comprises a portion of the polarizer 20.

The liquid crystal cell 12 comprises the liquid crystal layer 18arranged between the first and second substrates 14 and 16, as shown inFIG. 1. The liquid crystal layer 18 is composed of liquid crystal of avertical alignment type. The liquid crystal cell 12 is subjected toalignment division. That is, the liquid crystal cell 12 includesstructures or slits provided on the electrode of at least one of thesubstrates, so that the state of alignment of liquid crystal moleculeson one side of the structure or slit is different from the state ofalignment of liquid crystal molecules on the other side of thisstructures or slits. Concerning the structures or the slits, it ispossible to use all the structures or the slits which have already beenexplained.

FIGS. 58A to 58C are views showing liquid crystal molecules 18 c, 18 d,18 e and 18 f in the four different states of alignment, and therelation between the applied voltage and the quantity of transmittinglight. FIG. 58A shows the states of alignment of the liquid crystalmolecules 18 c, 18 d, 18 e and 18 f when a relatively low voltage, forexample a voltage V1, shown in FIG. 58C, is applied and the image areais viewed in the normal direction. FIG. 58B shows the states ofalignment of the liquid crystal molecules 18 c, 18 d, 18 e and 18 f whenthe same voltage V1 is applied and the image area is viewed in anoblique direction. In FIG. 58C, curve TA is a T-V curve of the alignmentof the liquid crystal molecules 18 c and 18 e in FIG. 58B, curve TF is aT-V curve of the alignment of the liquid crystal molecules 18 d and 18 fin FIG. 58B, and curve TN is a T-V curve of the averaged alignment ofall liquid crystal molecules in FIG. 58A. As can be seen in FIG. 58C,when a relatively low voltage V1 is applied and the image area is viewedin an oblique direction, the brightness becomes higher than that of acase in which the image area is viewed in the normal direction. In thecase where the relatively low voltage V1 is applied, it is intended thata relatively dark display with respect to gradation or gray scale isrealized, but the display becomes whitish at a certain viewing angle.This phenomenon becomes remarkable in the case where the viewing angleimproving film 62 is included.

The liquid crystal display device 10 shown in FIG. 56 is suitable forsolving the above problems by providing a specific direction lightscattering film 60. By the specific direction light scattering film 60,light is scattered in one specific direction, and light is scatteredonly slightly in the other directions. An example of the specificdirection light scattering film 60 is Nimisty manufactured by SumitomoKagaku Co.

FIG. 57A shows a case in which the liquid crystal display device 10having no specific direction light scattering film 60 is viewed in anoblique direction, and FIG. 57B is a view showing a case in which theliquid crystal display device 10 having the specific direction lightscattering film 60 is viewed in an oblique direction. In the case shownin FIG. 57A, light, which obliquely transmits through the liquid crystalcell 12, enters a viewer's eye. In this case, the viewer sees a whitishdisplay as described above. In the case shown in FIG. 57B, light madeincident to the specific direction light scattering film 60 in thenormal direction is scattered in an oblique upper direction. Therefore,light, which is transmitted through the liquid crystal cell 12 in thenormal direction, and light, which is obliquely transmitted through theliquid crystal cell 12, enter the viewers eye at the same time.Accordingly, it is possible for the viewer to see the image area in thesubstantially same condition as that of a case in which the viewer seesthe image area in the normal direction. In order to reduce the parallaxbetween the light, which is transmitted through the liquid crystal cell12 in the normal direction, and the light, which is obliquelytransmitted through the liquid crystal cell 12, it is preferable thatthe specific direction light scattering film 60 is arranged close to thepolarizer 20 on the emergent side of light.

The viewing angle improving film 62 is, for example, the retardationplate (λ/4 plate) 24 and 26 described in the above embodiment. When thepolarizers 20 and 22 and the retardation plates (λ/4 plate) 24 and 26are combined with each other, a circular polarization is created and thebrightness is enhanced as described above. In this connection, in thearrangement shown in FIG. 56, the viewing angle improving film 62 isprovided only on one substrate 14, however, of course, the viewing angleimproving film 62 may be provided on the other substrate 16. Further,the viewing angle improving film 62 may be one of the films 48, 50, 52,54 and 56 shown in FIGS. 39 to 53. That is, the viewing angle improvingfilm 62 is composed of a uniaxial oriented film, a biaxial oriented filmor a film having a negative retardation.

FIG. 59 is a view showing a variation of the liquid crystal displaydevice shown in FIG. 56. In FIG. 56, the specific direction lightscattering film 60 is arranged close to the polarizer 20 on the emergentside of light, and the viewing angle improving film 62 is arranged closeto the substrate 14. On the other hand, in FIG. 59, the specificdirection light scattering film 60 is arranged close to the substrate14, and the viewing angle improving film 62 is arranged close to thepolarizer 20 on the emergent side of light. The action of thisembodiment is the same as that of the embodiment shown in FIG. 59.

Concerning the position at which the specific direction light scatteringfilm is arranged, when the viewing angle improving film is arrangedclose to the liquid crystal layer and the light scattering film isarranged between this viewing angle improving film and the polarizingfilm, an especially good viewing angle characteristic is provided.Essentially, the viewing angle improving film is provided for cancellingthe optical effect of the liquid crystal with respect to light madeobliquely incident to the liquid crystal layer. However, when the lightscattering film is arranged close to the liquid crystal layer, lightmade perpendicularly incident to the crystal layer is scattered andobliquely passes through the viewing angle improving film. In this case,although light made perpendicularly incident to the liquid crystal layeris not subjected to an optical action by the liquid crystal layer, theviewing angle improving film exhibits an optical effect. That is, itacts so that leakage of light is caused, which makes matters worse.

FIG. 61 is a view showing a liquid crystal display device of the fifthembodiment. FIG. 62 is a view for explaining polarizing axes of thepolarizers and optical axes of the retardation plates of the liquidcrystal display device shown in FIG. 61. The liquid crystal display 10includes a liquid crystal cell 12, first and second polarizers 20 and22, and first and second retardation plates 24 and 26. Each of the firstand second retardation plates 24 and 26 has an optical axis 24A or 26Ain a plane parallel to the surfaces of the substrate, and theretardation is substantially λ/4. The optical axis 24A of the firstretardation plate 24 is perpendicular to the optical axis 26A of thesecond retardation plate 26. The polarizing axes 20A and 22A of thefirst and second polarizers 22 and 22 are arranged at an angle of 45°with respect to the optical axes 24A and 26A of the first and secondretardation plates 24 and 26. Voltage is applied between the electrodes28 and 32.

The liquid crystal cell 12 has a liquid crystal layer 18 interposedbetween the first and second substrates 14 and 16. The liquid crystallayer 18 comprises liquid crystal droplets 70 dispersed in a resin 72.The liquid crystal display device having the liquid crystal layer 18,which is made of the liquid crystal droplets 70 and the resin 72, isreferred to as a polymer dispersed type liquid crystal display device.However, it should be noted that the present invention is not limited tothe polymer dispersed type liquid crystal display device, but thepresent invention can be applied to another type liquid crystal displaydevice having a liquid crystal layer 18 in which the liquid crystaldroplets 70 coexist in the resin 72.

FIG. 63 is a view showing a state of alignment of liquid crystalmolecules in the liquid crystal droplets 70 when voltage is not applied.Liquid crystal molecules are aligned in all alignment directions. Whenvoltage is applied in this state, the liquid crystal molecules arealigned in the liquid crystal droplets 70 perpendicularly to thesubstrate surface.

FIG. 64 is a view showing a display in the state of alignment of theliquid crystal molecules shown in FIG. 63 when voltage is not applied.The liquid crystal molecules are aligned substantially at random withrespect to the substrate surface. Therefore, when the polarizers 20 and22 are arranged in a Cross Nicol and the λ/4 plates are arranged, awhite display is created.

FIG. 65 is a view showing a conventional liquid crystal display devicehaving the polarizers 20 and 22, but no retardation plates 24 and 26. Asshown in FIG. 63, the liquid crystal molecules are aligned in allaligning directions in the liquid crystal droplets 70 a, and theabsorbing axes 20A and 22A of the polarizers 20 and 22 are arrangedperpendicular to each other. Therefore, in a portion in which the liquidcrystal molecules are aligned in the same direction as the absorbingaxes 20A and 22A, the display becomes black, which is the same as theblack lines 36 in FIGS. 4 and 9.

According to the present invention, it is possible to erase a blackdisplay portion shown in FIG. 65, to realize a bright display shown inFIG. 64, by providing the retardation plates 24 and 26.

In order to realize the polymer dispersed type liquid crystal panel, anattempt is made in such a manner that fluorine resin and anultraviolet-ray curable type resin are mixed with each other by a mixingratio of 8:2 so that the size of liquid crystal droplets could beincreased to as large as possible. It is possible to use liquid crystalhaving positive dielectric constant anisotropy. Alternatively, it isalso possible to use liquid crystal having negative dielectric constantanisotropy. In the case where liquid crystal having positive dielectricconstant anisotropy is used, it is desirable that the liquid crystalmolecules lie down when voltage is not applied. Therefore, it isunnecessary to coat an alignment film, and a mixture of the liquidcrystal with the resin is filled into between the substrates which havebeen washed. In the case where liquid crystal having negative dielectricconstant anisotropy is used, the liquid crystal molecules lie down whenvoltage is applied. Therefore, when voltage is not applied, it isnecessary for the liquid crystal molecules to be aligned in the verticaldirection. Due to the foregoing, a polyimide film having the verticalalignment property is coated on the substrate.

After the mixture of liquid crystal with resin is filled, ultravioletray is irradiated so that the resin is cured. In this process, theliquid crystal and the resin are separated from each other and thedroplets 70 of liquid crystal are formed.

FIG. 66 is a view showing a liquid crystal display device of the sixthembodiment of the present invention. FIG. 67 is view for explainingpolarizing axes of the polarizers and optical axes of the retardationplates of the liquid crystal display device shown in FIG. 66. The liquidcrystal display device 10 includes a liquid crystal cell 12, first andsecond polarizers 20 and 22, and first and second retardation plates 24and 26. Each of the first and second retardation plates 24 and 26 has anoptical axis 24A or 26A in a plane parallel to the surfaces of thesubstrates, and the retardation is substantially λ/4. The optical axis24A of the first retardation plate 24 is perpendicular to the opticalaxis 26A of the second retardation plate 26. The polarizing axes 20A and22A of the first and second polarizers 20 and 22 are arranged at anangle of 45° with respect to the optical axes 24A and 26A of the firstand second retardation plates 24 and 26. Voltage is applied between theelectrodes 28 and 32.

The liquid crystal cell 12 includes a liquid crystal layer 18 arrangedbetween the first and second substrates 14 and 16. The liquid crystallayer 18 comprises a liquid crystal 74 dispersed in a polymer network76. The liquid crystal display device having the liquid crystal layer18, which is composed of the liquid crystal 74 and the polymer network76, is referred to as a polymer network type liquid crystal displaydevice. The liquid crystal is a vertical aligning type liquid crystalhaving a negative dielectric constant anisotropy. The first substrate 14is a color filter substrate, and the second substrate 16 is a TFTsubstrate.

In the alignment division using the vertical alignment type liquidcrystal and the linear structures 30 and 34 and the slits 38 asdescribed above, the problem that when a portion of the liquid crystalmolecules and the polarizing axes of the polarizers coincide with eachother in the case of application of voltage, the brightness is loweredmay be encountered, and therefore, the retardation plates (λ/4) areprovided so that the brightness can be enhanced. However, in the casewhere this technique is applied to an image area of a notebook typepersonal computer, the image area of which must be brighter, if thereare provided linear structures 30 and 34 and slits 38 in the displayregion, the ratio of opening of the display region is decreased, and itbecomes impossible to provide a sufficiently high brightness. Therefore,when the linear structures 30 and 34 and the slits 38 are provided onlyon the bus lines and the subsidiary capacitor lines, the ratio ofopening of the display region is increased, and it becomes possible toprovide a sufficiently high brightness. However, in this case, aninterval between the linear structures 30 and 34 or an interval betweenthe linear structure 30 and the slit 38 is extended too long, and ittakes long time for the inclination of crystals to be spread. As aresult, the speed of response is lowered. This problem can be solved bythis embodiment.

The polymer network 76 is formed so that the pretilt of liquid crystalmolecules of the liquid crystal 74 and the direction of inclination ofthe liquid crystal molecules in the case of application of voltage canbe regulated, which is referred to as a polymer stabilization. Thepolymer network 76 is a structure of polymerization which is made when aliquid crystal type or a non-liquid crystal type monomer is polymerizedby the action of ultraviolet rays or heat. This polymer network 76 issolidified as a structure having a specific alignment in the process ofpolymerization. Accordingly, in the polymer network 76, when the liquidcrystal molecules of the liquid crystal droplets 74 are alignedsubstantially in the vertical direction being accompanied by pre-tiltand voltage is applied to the liquid crystal molecules, the liquidcrystal molecules are inclined in the direction (pre-tilt direction),which is regulated by the polymer network 76, with a quick response.

The monomer composing the polymer network 76 is made of an ultravioletcurable type or thermo-setting type monomer. It is preferable that themonomer composing the polymer network 76 is a two functional acrylate ora mixture in which a two functional acrylate and a single functionalacrylate are mixed with each other. It is preferable that the pre-tiltangle of the liquid crystal molecules regulated by the polymer network76 is not less than 80°.

Stabilization treatment of the polymer network 76 is conducted by themethod shown in FIG. 68. The liquid crystal cell 12 is composed in sucha manner that the liquid crystal monomer is inserted between a pair ofsubstrates 14 and 16. While voltage is being applied upon the electrodes28 and 32 of the liquid crystal cell 12, the liquid crystal cell 12 isirradiated with ultraviolet rays (UV), so that the liquid crystalmonomer is subjected to optical polymerization. In this way, the liquidcrystal monomer is polymerized. Since polymerization is conducted whilevoltage is being applied, the liquid crystal molecules are alignedtoward the linear structures 30 and 34 and the slits 38 in the samemanner as that of a usual alignment division type liquid crystal displaydevice.

When the application of voltage, which is conducted for stabilizationtreatment, is stopped, the liquid crystal molecules are regulated by thesolidified polymer and kept in a state of alignment of predetermineddirections. In this way, the liquid crystal is pretilted. In this case,even if the linear strictures 30 and 34 and the slits 38 are notprovided, the bus lines and the protrusions of the subsidiary capacitorelectrodes function in the same manner as that of the linear structures30 and 34 and the slits 38. Therefore, the liquid crystal is pre-tilted.In this case, the behavior of the liquid crystal molecules is notaffected by the speed of response. Therefore, the liquid crystalmolecules may be pre-tilted while a relatively long period of time isbeing spent for the process of pretilt.

In this connection, although the polymer network 76 is set into a stateof solidification, it is not a perfect solid body. Therefore, whenvoltage is applied upon the polymer network 76 in the use of the liquidcrystal display device, the liquid crystal molecules are inclined withrespect to the substrate surfaces according to the pre-tilt. At thistime, the entire liquid crystal molecules are already pre-tilted.Therefore, the speed of response is high.

The pre-tilt angle depends upon a quantity of monomer to be added, anoptical polymerization starting agent, a quantity of irradiatedultraviolet rays and an applied voltage. In order to keep thecharacteristic of the vertical alignment type liquid crystal, it ispreferable that the pre-tilt angle is not less than 80°.

FIG. 69 is a graph showing the relation between the gradation and thespeed of response in the case where the liquid crystal display device isused. Curve X shows a speed of response in the case of the presentinvention, and curve Y shows a speed of response in the case where thepolymer network 76 is not subjected to stabilization treatment. Theliquid crystal monomer is 1.8 weight %, and the applied voltage forstabilization is 5.4 V. According to the present invention, the responseproperty for displaying of the liquid crystal display device isconsiderably enhanced.

FIGS. 70A to 70D are views showing a structure for the alignmentdivision of the liquid crystal display device shown in FIG. 66. Thecolor filter substrate 14 and TFT substrate 16 are provided withelectrodes 28 and 32 and vertical alignment films 29 and 33. Althoughthe alignment films are not shown in the above embodiments, thealignment films similar to the vertical alignment films 29 and 33 shownin FIG. 70 are provided. Further, the gate bus lines 40 and thesubsidiary capacity electrodes 46 are shown in FIG. 70.

In the structure shown in FIG. 70A, there are provided no linearstructures 30 and 34 and slits 38. In the stabilization treatment ofthis case, the gate bus lines 40 and the auxiliary capacitor electrodes46 act as protruding structures. In FIG. 70B, the linear structures 30are provided only on the color filter substrate 14. The linearstructures 30 are provided at positions corresponding to the subsidiarycapacity electrodes 46. Therefore, the linear structures 30 do not havean influence on the ratio of opening of the display region.

In FIG. 70C, the linear structures 30 are provided on the color filtersubstrate 14, and the linear structures 34 are provided on the TFTsubstrate 16. The linear structures 30 are provided at positionscorresponding to the subsidiary capacity electrodes 46, and the linearstructures 34 are provided at positions corresponding to the gate buslines 40. Therefore, they do not affect the ratio of opening of thedisplay region.

In FIG. 70D, the linear structures 30 are provided on the color filtersubstrate 14, and the slits 38 are provided on the TFT substrate 16. Thelinear structures 30 and the slits 38 are arranged at intervals shorterthan those of the embodiment shown in FIG. 70C. For example, the linearstructures 30 and the slits 38 can be arranged by the pattern shown inFIG. 38 or other patterns.

As explained above, according to the present invention, it is possibleto provide a liquid crystal display device of high brightness by which aviewer is capable of viewing an excellent image area over a wide viewingangle.

1. A liquid crystal display device comprising: a liquid crystal cellcomprising a pair of substrates and a liquid crystal layer arrangedbetween the pair of substrates, the liquid crystal of the liquid crystalcell being of a vertical alignment type; first and second polarizersarranged on either side of the liquid crystal cell; a first retardationplate arranged between the liquid crystal cell and the first polarizer;a second retardation plate arranged between the liquid crystal cell andthe second polarizer; each of the first and second retardation plateshaving an optical axis in a plane parallel to the surfaces of thesubstrates and a retardation of substantially λ/4, the optical axis ofthe first retardation plate being perpendicular to the optical axis ofthe second retardation plate, the negative retardation ((nx+ny) /2−nz)of each of the retardation plates being approximately zero; a firstoptical plate arranged on or near the liquid crystal cell and havingrefractive indices in the relationship of nx=ny>nz, the first opticalplate having a retardation the value of which is identical to that ofthe liquid crystal layer and the sign of which is reverse to that of theliquid crystal layer; a second optical plate having refractive indicesin the relationship of nx=ny<nz, said second optical plate or a partthereof being arranged on or near the first polarizer; and a thirdoptical plate arranged on or near the second polarizer and havingrefractive indices in the relationship of nx>ny=nz.
 2. A liquid crystaldisplay device according to claim 1, wherein the retardation of thesecond optical plate is not less than 80 nm and not more than 300 nm. 3.A liquid crystal display device according to claim 1, wherein theretardation of the third optical plate is not less than 25 nm and notmore than 160 nm.